GREENE COUNTY, PA Revised Preliminary DFIRM Mapping April 10, 2013 Kevin Donnelly, P.E., CFM GG3, Greenhorne & O Mara, Inc.
Presentation Agenda Greene County DFIRM Overview September 30, 2010 DFIRM Countywide Format Vertical Datum Conversion Base Map Data New Floodplain Boundaries Incorporated Letters of Map Revision (LOMRs) GIS Products and Access Revised Preliminary Studies March 1, 2013 Base Level (Approximate) Studies Preliminary FIS and DFIRM Revisions
Base Map + Terrain Data + Flood Hazard Data
A DFIRM is Hardcopy Map and Flood Insurance Study (FIS) report Digital Flood Hazard Data Standard GIS database Horizontally and vertically controlled (known C.S.)
Countywide Format Countywide Production (26 communities) 1 Volume Flood Insurance Study (FIS) Report 21 effective FIS reports reduced to one volume New DFIRM Index based on USGS Quads Two map panel scales 1:6,000 - detailed studied streams (Zone AE) 1:12,000 - approximate studied streams (Zone A)
Countywide FIS Report Production Countywide Compilation Combined hazard information into a seamless countywide format Re-stationing and Re-lettering of Cross Sections Flood Profiles and Floodway Data Tables Vertical Datum Conversion (NGVD29 to NAVD88) Combined Effective FIS Reports 21 Effective FIS Reports combined into one countywide report
Vertical Datum Conversion NGVD 29 (old) Based on a mean sea level from 21 tidal stations in the US & 5 stations in Canada NAVD 88 (new) Based on the density of the Earth instead of varying values of sea heights Conversion in Greene County Varies NGVD29 + (vertical adjustment) = NAVD88 The vertical datum adjustment is 0. 446 ft (negative) See page 19-20 of FIS for more information
Vertical Datum Conversion (-0.446 ft) NGVD 29 (old) NAVD 88 (new) 6 4 2 0 BFE = 4 ft 0.446 ft BFE = 3.554 ft 6 4 2 0
Base Mapping GIS Data Orthoimagery PAMAP program (1:19,200 scale and 1-ft ground resolution) Flown in Spring 2006 (Color to B/W) Transportation Road names from GIS data provided by PENNDOT and Effective FIRMs Stream Centerlines Developed from LiDAR data and Orthoimagery Vector lines with more than 1 square mile of drainage Stream names taken from USGS National Hydrography Dataset (NHD) and effective FIRMs
Base Mapping GIS Data Political Boundaries PENNDOT political boundaries NGS Benchmarks First or Second Order Vertical Benchmarks Stability C or better http://www.ngs.noaa.gov
Floodplain Boundary Changes Sept. 30, 2010 No New Detailed Riverine Engineering Studies Detailed Studies (Zone AE w/ BFEs) Re-delineation of approximately 46 stream miles using PAMAP LiDAR Approximate Studies (Zone A) New Hydrologic and Hydraulic analyses along 374 stream miles USGS Regression Equations (SIR 2008-5102) and HEC-RAS Flood boundaries mapped using PAMAP LiDAR
Redelineation (Zone AE w/bfes)
Approximate Zone A Floodplain
Improved Zone A Mapping
Improved Zone A Mapping
One Incorporated LOMR a South Fork Tenmile Creek, Waynesburg, PA (Township of Franklin) a 09-03-0260P
DFIRM GIS Products and Access Preliminary DFIRMs, FIS, Fact Sheets & Ordinance Level Information http://www.rampp-team.com/public.htm GIS files in a standard DFIRM database Shapefile (*.shp), Coverage (*.e00), MapInfo (*.mif) National Flood Hazard Layer (NFHL) KMZ, WMS, shapefiles Georeferenced FIRM panel images Map Store (http://msc.fema.gov) Download products: GIS database, FIS reports (pdf format), Georeferenced FIRM panels, FIRMettes Mapping Information Platform (MIP) https://hazards.fema.gov Digital Repository (Engineering Backup and DFIRM data) DFIRM Web Viewer and Training Materials Available after Effective Date (preliminary flooding available upon request)
NFHL and Google Earth NFHL Flood Hazard Zones/floodways BFEs Community Names/Boundaries Coastal Barrier Resources System Hydraulic and Flood Control Structures Cross Sections and Coast Transects (with labels) LOMRs
Revised Preliminary Study New Base Level (Approximate) Study Methodology PA Fork Dunkard Creek Pumpkin Run Ruff Creek Toms Run Studies were conducted based on priority needs and funding
Base Level (Approximate) Studies Survey No Survey Performed Hydrology Peak Discharge Regression equations from USGS Scientific Investigations Report 2008-5102 Hydraulic Modeling HEC-RAS v4.1 steady flow model Channel and overbank cross section geometry from PAMAP LiDAR Impact of structures (Bridges, Culverts, etc.) not considered No floodways modeled Water surface elevations computed for the 1% annual chance event (100-yr) Floodplain Mapping Delineated using PAMAP LiDAR
Preliminary FIS and DFIRM Revisions Flood Insurance Rate Maps Additional floodplain delineations
Additional information regarding FIS reports, fact sheets, and FIRM index panels can be found at: http://www.rampp-team.com/public.htm
Questions?